The isolation of metaphase chromosomes from teratocarcinoma cell lines will continue. Isolation of teratocarcinomas from an inbred line with a distinctive chromosomal translocation will begin. We will study a number of aspects of differentiation in early mouse embryos, i.e. the role of plasminogen and plasminogen activators, the effect and mode of action of retinoic acid and vitamin A derivatives, and the control of alphafetoprotein production. We will be completing work on a lambda EK-2 vector and problems of phage injection and prophage complementation.